This invention relates to fluid pressure regulating systems, including systems for measuring gas pressure and for controlling the pressure of the gas. The invention further relates to wound drainage systems for draining fluids from medical patients, such as from the chest cavity, by means of gas pressure differentials using low pressure gas systems.
In many situations involving gases, it is important and often mandatory to measure the pressure of the gas. A typical example of the need to measure gas pressure exists in hospitals, where the vacuum or suction distributed in the hospital from a central vacuum supply must be monitored as it is used. Such suction is used, for example, in conjunction with wound drainage devices, where fluids such as blood, water and gas from a wound victim's pleural cavity are withdrawn using a pressure differential established between the suction source and the internal pressure in the victim. Such suction pressure and pressure differentials must be precisely measured because of the dangerous conditions which could result if unduly high or low pressure differentials should occur. In this application as in many other pressure measuring applications, it is desirable to incorporate a pressure measuring device which is compact, which makes the pressure measurements with precision, which is capable of functioning reliably for long periods of time, and which is economical to manufacture. Presently available gas pressure measuring devices which have the desired reliability and precision are generally expensive because of their intricacy or bulk due to their incorporation of manometer tubes. Wound drainage systems incorporating manometers having water whose level indicates fluid pressure are inconvenient because of the need to add water prior to use, as well as because of their size and weight.
For many years, a standard apparatus for performing the evacuation of the pleural cavity was an underwater seal drainage system known as the "3-bottle set-up". The 3-bottle set-up consists of a collection bottle, a water seal bottle and a suction control bottle. A catheter runs from the patient's pleural cavity to the collection bottle, and the suction bottle is connected by a tube to a suction source. The three bottles are connected in series by various tubes to apply a predetermined suction to the pleural cavity to withdraw fluid and air, and discharge the same into the collection bottle. Gases entering the collection bottle bubble through water in the water seal bottle. The water in the water seal also prevents the back flow of air into the chest cavity.
The 3-bottle set-up lost favor with the introduction of an underwater seal drainage system sold under the name "Pleur-evac" in 1966 by Deknatel Inc., the predecessor of the Deknatel Division of Howmedica Inc. U.S. Pat. Nos. 3,363,626; 3,363,627; 3,559,647; 3,683,913; 3,782,497; 4,258,824; and Re. 29,877 are directed to various aspects of the Pleur-evac system which has been marketed over the years. The Pleur-evac system provided improvements that eliminated various shortcomings of the 3-bottle set-up. These improvements have included the elimination of variations in the 3-bottle set-up that existed between different manufacturers, hospitals, and hospital laboratories, such variations including bottle size, tube length and diameter, stopper material and the like. Various inefficiencies and dangers have existed in the 3-bottle set-up resulting from the many separate components and the large number (usually 16 or 17) of connections, such as pneumothorax which may result from the loss of the water seal in the water seal bottle if suction were temporarily disconnected, and possible build-ups of positive pressure which could cause tension pneumothorax and possible mediastanal shift. Another serious shortcoming of the 3-bottle set up is danger of incorrect connection and the time necessary to set the system up and to monitor its operation.
Among the features of the Pleur-evac system which provide its improved performance are employment of 3-bottle techniques in a single, pre-formed, self-contained unit. The desired values of suction are established by the levels of water in the suction control bottle and the water seal bottle, which levels are filled according to specified values prior to the application of the system to the patient. A special valve referred to as the "High Negativity Valve" is included which floats closed when the patient's negativity becomes sufficient to threaten loss of the water seal. Also, a "Positive Pressure Release Valve" in the large arm of the water seal chamber works to prevent a tension pneumothorax when pressure in the large arm of the water seal exceeds a prescribed value because of suction malfunction, accidental clamping or occlusion of the suction tube. The Pleur-evac system is disposable and helps in the battle to control cross-contamination.
Despite the advantages of the Pleur-evac system over the 3-bottle set-up and the general acceptance of the device in the medical community, there has remained a continuing need to improve the convenience and performance of chest drainage systems and to render such systems very compact. Underwater seal drainage systems as described above require the filling of manometer tubes to levels specified by the physician prior to being connected to the patient and the hospital suction system. Although it is conceivable that such filling could be performed at a manufacturing facility prior to shipment, as a practical matter this would not suffice because frequent adjustments are needed according to the different values of patient suction as dictated by the attending physician. Moreover, the presence of fluid in the various tubes could result in damage to the system during shipment such as because of freezing temperatures or because of leakage. In addition, accuracy of present underwater drainage systems is limited in that the filling of the manometers and the reading of the various gauges must be done visually by observing the liquid level in the respective chambers. A reduction in size of the system would offer such benefits as ease of use, ease of storage, less expensive shipping costs, and the reduction in the obstruction between the patient, his or her visitors and the medical staff.